In one form of rivet setting tool for setting screwthreaded rivet nuts or blind rivet nuts, referred to hereinafter for the sake of simplicity as rivet nuts, the tool comprises a forward feed arrangement for imparting an axial movement to the screw-threaded pin or tensile pin, the forward feed arrangement being actuable to perform the rivet nut upsetting operation. The forward feed arrangement comprises a piston cylinder assembly including a pressing piston and a working piston.
In such a tool, the working movement of the pressing piston and the working piston is produced by an external compressed air source, while the return movement of those pistons is produced by springs. The springs required for that purpose are disadvantageous from various points of view. Apart from the fact that the spring force may gradually become weaker due to fatigue in the course of a prolonged period of time or the springs may even become defective, for example they may break, so that the pistons are then no longer satisfactorily returned, there is also the problem that springs of suitable quality are very expensive and also give rise to further labour costs in assembly of the tool. Furthermore, a spring can only exert a given force so that that consideration also limits the speed at which the return movement of the pistons may be effected.